Wireless relay station for radio frequency-based tracking system

ABSTRACT

System and methods of tracking a position of a mobile device with an electromagnetic signal-transmitting antenna include receiving electromagnetic signals from the transmitting antenna of the mobile device by a plurality of receiver antennae of a base station and by one or more receiver antennae of a relay station. The relay station transmits to the base station timing information associated with the electromagnetic signals received by the one or more receiver antennae of the relay station. The base station computes a position of the transmitting antenna of the mobile device based on timing information computed from the electromagnetic signals received by the plurality of receiver antennae of the base station and on the timing information received from the relay station.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/961,274, filed Apr. 24, 2018, titled “Wireless Relay Station forRadio Frequency-Based Tracking System,” which is a divisional ofpatented U.S. patent application Ser. No. 15/291,364, filed Oct. 12,2016, titled “Wireless Relay Station for Radio Frequency-Based TrackingSystem,” U.S. Pat. No. 9,961,503, issued May 1, 2018, which is acontinuation of patented U.S. patent application Ser. No. 14/597,360,filed Jan. 15, 2015, titled “Wireless Relay Station for RadioFrequency-Based Tracking System”, U.S. Pat. No. 9,497,728, issued Nov.15, 2016, which claims the benefit of and priority to U.S. provisionalapplication No. 61/928,496, filed Jan. 17, 2014, titled “Wireless RelayStation for Radio Frequency-Based Tracking System,” the entireties ofwhich applications are incorporated by reference herein.

FIELD OF THE INVENTION

The invention relates generally to systems and methods for tracking theposition of electromagnetic signal transmitting devices. In particular,the invention relates to radio frequency (RF)-based wireless positiontracking systems that use one or more wireless relay stations.

BACKGROUND

Position tracking systems can use a variety of configurations fortracking the two- or three-dimensional position of a wireless device. Inmany arrangements, a system may require three or more base receivers (orthree or more base antennae connected to a single base receiver) toreceive some form of data from a wireless device and use that data tocalculate the position of the device. The data can be timinginformation, signal strength, or angle of arrival measurements of thesignal transmitted by the device and received at the base receiver(s)antennae of the system. In all arrangements, the position of the basereceiver antennae of the system is important for calculating theposition of the device and often these antennae are wired to the systemfor computing the position of the device.

Over the years, several different forms of tracking systems have evolvedwith the most notable being Global Positioning System or GPS. For GPS,the mobile receiver uses timing information sent from satellites andthen calculates the position of the GPS receiver with the mobilereceiver doing the position computation using the timing informationfrom the satellite signals.

SUMMARY

All examples and features mentioned below can be combined in anytechnically feasible way.

Embodiments of position-tracking systems described herein, unlike GPS,perform position calculation using signals sent from the wireless devicebeing tracked. This allows the device to be simple, but does add somecomplexity to the position-tracking system. The position-trackingsystems use one or more wireless relay stations communicating with abase station which uses multiple receive locations of the wireless relaystations as coordinate references for performing timing and positioningcalculations on a wireless device communicating with the base stationand the wireless relay stations. By incorporating one or more wirelessrelay stations, the system can improve setup options, improve accuracyand provide a larger working volume for the wireless device.

One example design for a position-tracking system for three-dimensionaltracking comprises at least four base receivers (or one base receiverwith four base antennae) wired to the base station. These base receiversreceive the wireless signals sent from the mobile wireless device beingtracked and send that information to the base station for positioncomputation. In one embodiment, the base receivers are fixed in positionin space and wired to the base station. However, this design can belimiting as the wired base receivers can reduce the working volume andincrease cost because they are tethered to the base station, makingspacing of their antennae more difficult and expensive to setup. Forexample, a wireless mouse tracked in three dimensions for interactionwith games or other interactive software programs can only be trackedwithin the working area defined by the spacing of the base receivers ofthe base station. If these base receivers or receiver antennae areplaced around a television, the working volume is defined by theposition of the base receivers, and accuracy may diminish as the devicebeing tracked moves away from the central point of the positions of thebase receivers. If the position-tracking system uses a device signal ofarrival time differential compared at each receiver (or antenna) formaking position calculations, this limited base receiver or receiverantenna spacing caused by a wired connection can be especially limiting.

A position-tracking system that incorporates one or more wireless relaystations to add additional measurements used for tracking by theposition-tracking system can significantly improve overposition-tracking systems requiring fully wired or tethered basereceivers together with their corresponding antennae. Receiving timinginformation from the device being tracked, each relay station can expandthe working volume or tracked area of the device and provide moreoptions for product integration and position-tracking system set up.Also, by expanding the distances between total receivers or receiverantennae, the position-tracking system can improve position accuracy,allowing more precise measurements.

Each relay station communicates wirelessly with both the device beingtracked and a base station performing the position tracking function.Alternatively, one or more relay stations can be wired to the basestation, with wires replacing the wireless communication channel. Inthat embodiment, each relay station is in a fixed position, such asplugged into an electrical outlet, or be battery powered. Duringinstallation, each transmitter of each relay station acts like one ormore “devices” communicating with the base station, and the base stationdetermines the position of that transmitter. This information locatesthe relay station with respect to the receiver antennae of the basestation. The base station also locates the position of each receiverantenna of a relay station with respect to the transmitter antennae ofthat relay station. Alternatively, relay stations can be placed at fixedknown positions to provide the base station with the known coordinatesfor making position calculations.

During normal (tracking) operation, the device being tracked transmitsthe signal used to generate timing information, this signal beingreceived at both the wired base antennae connected to the base stationand the wireless relay station(s) receiving antenna(e). The relaystation can be equipped with at least two receivers or receiver antennaeand uses the multiple receive points provided by these separatereceivers or antennae to compare timing differences in the device signalarrival at each receiver or receiver antenna. As the signal is receivedat the relay station, the time difference of arrival (or, equivalently,the phase difference of arrival) is calculated between both (or more)receivers or receiver antennae in the relay station. Because phase (θ)and time (t) are related by θ=ωt, where ω is a scalar, phase and timeare equivalent systems and subsequent descriptions may be denoted bytime or time differences, as appropriate.

This timing data calculated by the relay station is sent to the basestation, preferably in a wireless manner, where the base station can usethat timing data from each relay station receiver or receiver antenna asadditional equations for calculating the position of the device. Bydoing timing comparisons and calculations at the relay station, theposition-tracking system can avoid a timing path error from the relaystation to the base station, thereby allowing the relay station to senddata that is unaffected by radio propagation and interferenceinstability, such as multipath on the round trip. Because interferencelike multipath is additive, removing one of the paths for this timingdata significantly improves system performance through the reduction ofmultipath effects. If the relay station is configured with a singletransceiver and antenna, techniques can reduce the effects ofinterference, such as implementing a duplex system whereby the receiverportion of the relay station transceiver receives at one spectrum, forexample, 2.4 GHz, and the return transmission from the same relaystation is at a different spectrum, for example, 5.8 GHz.

Whereas using the same antenna for both receiving and transmitting isoptimal, it may not be trivial or cost effective to multiplex thecircuitry attached to this antenna to achieve both functions in areal-time manner. Another technique is to place the receiver andtransmitter antenna concentrically, so that they share the same origin.Designs for concentric antenna, however, may be difficult to implement.

In one embodiment, the relay station is equipped with at least tworeceivers, or receiver antennae, and uses two transmitters to retransmitthe phase information of the device, properly coded and correlated toits signal arrival at the relay station receivers or receiver antennae.The relay station sends this phase/timing information to theposition-tracking system using any of a variety of means. Thistransmission can be accomplished directly with common or additionalwireless signal channels. These signal channels can communicatewirelessly on a different frequency channel, for example, by usingdifferent encoding. This transmission can also be sent using powerlinecommunication. Preferably, the transmission is sent at a compatiblefrequency over one or both transmitter channels employed by thetransmitter(s) of the relay station.

In one aspect, a method of tracking a position of a mobile device withan electromagnetic signal-transmitting antenna include receivingelectromagnetic signals from the transmitting antenna of the mobiledevice by a plurality of receiver antennae of a base station and by oneor more receiver antennae of a relay station. The relay stationtransmits to the base station timing information associated with theelectromagnetic signals received by the one or more receiver antennae ofthe relay station. The base station computes a position of thetransmitting antenna of the mobile device based on timing informationcomputed from the electromagnetic signals received by the plurality ofreceiver antennae of the base station and on the timing informationreceived from the relay station.

In another aspect, a position-tracking system comprises a base stationwith a processor, at least three spatially separated receiver antennaedisposed at locations known to the processor of the base station. Eachof the at least three receiver antennae receive electromagnetic signalstransmitted by a transmitting antenna of a mobile device. Theposition-tracking system further comprises one or more relay stations incommunication with the base station and with the transmitting antenna ofthe mobile device. Each relay station is disposed at a distance from thebase station known to the processor of the base station. Each relaystation comprises a processor, one or more receiving antennae thatreceive the electromagnetic signals transmitted by the transmittingantenna of the mobile device, and one or more transmitter antennae. Thetransmitter antennae of each relay station send timing information tothe base station associated with the electromagnetic signals received bythe one or more receiver antennae of the relay station. The processor ofthe base station uses the timing information received from the one ormore relay stations and the timing information associated with theelectromagnetic signals received by the at least three receiver antennaeof the base station to compute the position of the transmitting antenna.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further advantages of this invention may be betterunderstood by referring to the following description in conjunction withthe accompanying drawings, in which like numerals indicate likestructural elements and features in various figures. The drawings arenot necessarily to scale, emphasis instead being placed uponillustrating the principles of the invention.

FIG. 1 is a block diagram of an embodiment of a position-trackingsystem, including a base station in communication with a relay station,for tracking the position of an electromagnetic signal transmittingdevice.

FIG. 2 is a diagram for illustrating position measurements based ondevice transmitter to base station receiver transmissions.

FIG. 3 is a diagram for illustrating position measurements based onrelay station transmitter to base station receiver transmissions.

FIG. 4 is a diagram for illustrating position measurements based ondevice transmitter to relay station receiver transmissions.

FIG. 5 is a flow diagram detailing embodiments of modes of the relaystation.

DETAILED DESCRIPTION

FIG. 1 shows an embodiment of a position-tracking system 10 comprisingbase station hardware (or simply base station) 12 in communication withmultiple base receivers or receiver antennae 14 (herein referred to,interchangeably, as receiver, receiving antenna, or receiver antenna 14)and with one or more relay stations 16 (only one shown), for trackingthe position of an electromagnetic signal (e.g., radio frequency)emitting transmitter or transmitter antenna 18 (herein referred to,interchangeably, as transmitter, transmitting antenna, or transmitterantenna 18). The transmitter antenna 18 is carried by, attached to, orembedded in a tracked object. Although only one transmitter antenna 18is shown, the object can have more than one tracked transmitter antenna18, to allow the orientation of the object to be calculated based ongeometric principles. For example, two transmitter antennae, separatedby a distance d, yield a pointer, because the two transmitter antennaeform a line with known direction. Three transmitter antennae provideenough information to calculate a three-dimensional orientation.

To track the position of a single transmitter antenna 18 in threedimensions (x, y, z), one embodiment of the position-tracking system 10has at least four receiver antennae 14. For two-dimensional positiontracking, the position-tracking system 10 may have as few as three basereceiver antennae 14. The base receiver antennae 14 are distinct andfixed in space, and provide a reference frame within which thetransmitter antennae 18 is tracked. In this example, the base receiverantennae 14 are disposed around a monitor 20. Additional base receiverantennae can provide better coverage and more accuracy, at the expenseof complexity and cost.

The configuration of the position-tracking system 10 can be reversed,with the base receiver antennae 14 being tracked and the transmitterantennae providing the reference frame. Alternatively, inertial sensorscould be integrated in the object with the wireless transmitter antenna18 being tracked to provide orientation.

The relay station 16 has two or more receivers or receiver antennae 22(herein referred to, interchangeably, as receiver, receiving antenna, orreceiver antenna 22) and two or more transmitters or transmittingantenna 24 (herein referred to, interchangeably, as transmitter,transmitter antenna, or transmitting antenna 24). The two or morereceiver antennae 22 are at known distances apart from each other andfrom the transmitting antenna 24. The position-tracking system 10 canhave multiple of such relay stations, with each additional relay stationthus adding at least two additional receiver antennae 22 to the system10. As noted above, additional receiver antennae provide better accuracyand coverage. These relay station receivers 22 provide the additionalcoverage for the position-tracking system 10 to minimize multipath andto increase range.

The relay station 16 is effectively a transceiver that, when acting as areceiver, provides additional information for a tracking algorithm usedby the base station 12 to compute the position of the transmitterantenna 18. The signal received by the relay station 16 are processed atthe relay station 16 (by the hardware portion of the relay station—notshown—that is part of the receiver) and re-transmitted to the basereceiver antennae 14. This transmission can be done by cables orwirelessly. The relay station 16 can function similarly to the basestation 12, whose operation is described below, to analyze a time ofarrival difference at the multiple receiver antennae 22 that are part ofthe relay station 16.

Alternatively, the relay station 16 can operate with a single receiverantenna 22, in which case the received signal from the wirelesstransmitter antenna 18 being tracked can either be instantaneouslyre-transmitted by the relay station 16 (MIMO) to maintain a timerelationship (provided the distance path between the relay station 16and each base receiver antenna 14 is fixed and known) or converted to adifferent frequency to avoid frequency collision or interference. MIMO(Multiple-Input Multiple-Output) systems use more than one transmitantenna to send a signal on the same frequency to more than one receiveantenna.

The relay station can be any one of a variety of mobile devices used forother functions, such as smart phones, tablets, or laptops, provided theposition of the relay station 16 is known or remains fixed in spaceduring position-tracking operation (i.e., when communicating with thebase station 12 and the mobile transmitter antenna 18).

FIG. 2 shows an example of operation of the position-tracking system 10using phase for timing comparisons. The base station 12 has a processor(not shown), such as a central processing unit or CPU, programmed toperform a position-tracking algorithm. The position-tracking algorithmis based on a best-fit of the time of flight measurements between thetransmitter antenna 18 with the object and the base receiver antennae14. An example implementation of the position-tracking algorithm isdescribed in U.S. application Ser. No. 14/354,833, filed on Apr. 28,2014, titled “Systems and Methods of Wireless Position Tracking,” theentirety of which application is incorporated by reference herein.

In this phase-based embodiment of the position-tracking system 10, thephase of the RF signal transmitted by the transmitter 18 is used tomeasure distance. A phase shift of 360° corresponds to one wavelength,and, by measuring the phase differences of the transmitter signalrecorded at two base receiver antennae 14, the distance is calculated.In the following equations (Eq.1-Eq. 4), r1, r2, r3, and r4 representdistances between the positions of the base receiver antennae 14 and theposition of the transmitter 18, and are represented by the phases.Receiver positions are denoted asrcvpos_(receiver number, position coordinate), and are fixed, knownquantities. Position coordinate 1, 2, 3 represent x, y, z, respectively.

$\begin{matrix}{{r\; 1} = \sqrt{\left( {{rcvrpos}_{1,1} - x_{1}} \right)^{2} + \left( {{rcvrpos}_{1,2} - x_{2}} \right)^{2} + \left( {{rcvrpos}_{1,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 1} \right) \\{{r\; 2} = \sqrt{\left( {{rcvrpos}_{2,1} - x_{1}} \right)^{2} + \left( {{rcvrpos}_{2,2} - x_{2}} \right)^{2} + \left( {{rcvrpos}_{2,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 2} \right) \\{{r\; 3} = \sqrt{\left( {{rcvrpos}_{3,1} - x_{1}} \right)^{2} + \left( {{rcvrpos}_{3,2} - x_{2}} \right)^{2} + \left( {{rcvrpos}_{3,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 3} \right) \\{{r\; 4} = \sqrt{\left( {{rcvrpos}_{4,1} - x_{1}} \right)^{2} + \left( {{rcvrpos}_{4,2} - x_{2}} \right)^{2} + \left( {{rcvrpos}_{4,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 4} \right) \\{\delta_{1,2} = {{r\; 1} - {r\; 2}}} & \left( {{Eq}.\mspace{14mu} 5} \right) \\{\delta_{1,3} = {{r\; 1} - {r\; 3}}} & \left( {{Eq}.\mspace{14mu} 6} \right) \\{\delta_{1,4} = {{r\; 1} - {r\; 4}}} & \left( {{Eq}.\mspace{14mu} 7} \right)\end{matrix}$

The differences between the phase measurements (δ's, Eq. 5-Eq.7), whichare calculated by the base station hardware, are used to solve for x1,x2 and x3, which represents the x, y, z positions of the devicetransmitter antenna 18, respectively. As is known in the art, this canbe solved in a least squares algorithm, such as Levenberg-Marquardt orin a Kalman filter. Also known in the art is that more rangemeasurements can be used to form an overdetermined solution, and alsoallows other methods to be used, such as weighted solutions, selecting asubset of equations, etc. These additional range measurements can beprovided for by the relay station 16.

FIG. 3 shows an example of transmissions from the relay station 16 tothe base receiver antennae 14. The relay station 16 resides at alocation where the relay station can improve in tracking the transmitter18. For example, this location may be on a wall, behind the user, on aceiling. Before data from the relay station 16 can be used to improveperformance, the position of the relay station 16 relative to the basestation 12 needs to be determined. Specifically, the positions of thereceiver antennae 22 of the relay station 16 need to be determined; thisinformation can reside at the base station 12.

To determine the positions of the receiver antennae 22, the transmitters24-1 and 24-2 are utilized in a first manner. These transmitters 24-1,24-2 operate like transmitter antenna 18, except that the transmitters24-1, 24-2 transmit at different frequencies from each other so thatthey can be differentiated from one another. The positions of thetransmitters 24-1, 24-2 are computed just like that of the transmitterantenna 18. The equations to compute these positions are similar toEq.1-Eq.7. The equations (Eq. 8-Eq. 14) for transmitter 24-1, which useranges r5, r6, r7, and r8, are:

$\begin{matrix}{{r\; 5} = \sqrt{\left( {{rptrpos}_{5,1} - x_{1}} \right)^{2} + \left( {{rptrpos}_{5,2} - x_{2}} \right)^{2} + \left( {{rptrpos}_{5,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 8} \right) \\{{r\; 6} = \sqrt{\left( {{rptrpos}_{6,1} - x_{1}} \right)^{2} + \left( {{rptrpos}_{6,2} - x_{2}} \right)^{2} + \left( {{rptrpos}_{6,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 9} \right) \\{{r\; 7} = \sqrt{\left( {{rptrpos}_{7,1} - x_{1}} \right)^{2} + \left( {{rptrpos}_{7,2} - x_{2}} \right)^{2} + \left( {{rptrpos}_{7,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 10} \right) \\{{r\; 8} = \sqrt{\left( {{rptrpos}_{8,1} - x_{1}} \right)^{2} + \left( {{rptrpos}_{8,2} - x_{2}} \right)^{2} + \left( {{rptrpos}_{8,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 11} \right) \\{\delta_{5,6} = {{r\; 5} - {r\; 6}}} & \left( {{Eq}.\mspace{14mu} 12} \right) \\{\delta_{5,7} = {{r\; 5} - {r\; 7}}} & \left( {{Eq}.\mspace{14mu} 13} \right) \\{\delta_{5,8} = {{r\; 5} - {r\; 8}}} & \left( {{Eq}.\mspace{14mu} 14} \right)\end{matrix}$

And the equations (Eq. 15-Eq. 21) for transmitter 24-2, which usesranges r9, r10, r11, and r12, are:

$\begin{matrix}{{r\; 9} = \sqrt{\left( {{rptrpos}_{9,1} - x_{1}} \right)^{2} + \left( {{rptrpos}_{9,2} - x_{2}} \right)^{2} + \left( {{rptrpos}_{9,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 15} \right) \\{{r\; 10} = \sqrt{\left( {{rptrpos}_{10,1} - x_{1}} \right)^{2} + \left( {{rptrpos}_{10,2} - x_{2}} \right)^{2} + \left( {{rptrpos}_{10,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 16} \right) \\{{r\; 11} = \sqrt{\left( {{rptrpos}_{11,1} - x_{1}} \right)^{2} + \left( {{rptrpos}_{11,2} - x_{2}} \right)^{2} + \left( {{rptrpos}_{11,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 17} \right) \\{{r\; 12} = \sqrt{\left( {{rptrpos}_{12,1} - x_{1}} \right)^{2} + \left( {{rptrpos}_{12,2} - x_{2}} \right)^{2} + \left( {{rptrpos}_{12,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 18} \right) \\{\delta_{9,10} = {{r\; 9} - {r\; 10}}} & \left( {{Eq}.\mspace{14mu} 19} \right) \\{\delta_{9,11} = {{r\; 9} - {r\; 11}}} & \left( {{Eq}.\mspace{14mu} 20} \right) \\{\delta_{9,12} = {{r\; 9} - {r\; 12}}} & \left( {{Eq}.\mspace{14mu} 21} \right)\end{matrix}$

These two sets of equations, (Eq. 8-Eq. 14) and (Eq. 15-Eq. 21) are usedseparately to solve for x1, x2 and x3, which represents the x, y, z,position, of each transmitter antenna 24-1 and 24-2, respectively.

After the positions of transmitters 24-1 and 24-2 are known, it isstraightforward to determine the positions of the receiver antennae 22.The two computed locations of the transmitter antennae 24-1 and 24-2provide reference points for determining the locations of the receiverantennae 22. Geometry and knowledge of the antennae layout provides thelocations of the receiver antennae 22. An example is to place receiverantenna 22 in a line between transmitter antenna 24-1 and 24-2. Thisprovides exact knowledge of where each receiver antenna 22 ispositioned. This calculation can be performed at the relay station 16 orat the base station 12. After these positions are determined, the secondmeans of use of transmitter antennae 24-1, 24-2 occurs. The relaystation 16 transmits this position information using the sametransmitter antennae 24-1, 24-2 using standard information transmissionmethods, such as used for cellular communication, Wi-Fi, etc., as isknown in the art. Both the base station 12 and the relay station 16contain standard circuitry for performing this operation and ismultiplexed in at the appropriate setup time while the position-trackingsystem 10 is in a setup mode.

In one alternative embodiment, the receiver antennae 22 and transmitterantennae 24 of the relay station 16 may be embodied in a single antennaeand transmission/receipt of signals can be separated by time orfrequency. In another alternative embodiment, the position of thetransmitter antennae 24 and receiver antennae 22 may be fixed usinganother device, such as a GPS or mobile phone with locating ability. Forexample, a user might determine the position of antennae 22 and 24 asderived from another device (GPS) and this information would betransmitted to the base station 12. Subsequently, as described above,the relay station 16 can provide tracking information for the devicetransmitter 18.

FIG. 4 illustrates the additional receiver paths between the transmitterantenna 18 and the relay station receiver antennae 22-1 and 22-2. Pathr13 and path r14 correspond to the distances between the transmitter 18and the receiver antennae 22-1 and 22-2, respectively. Relay stationreceiver positions are denoted asrptrpos_(receiver number,position coordinate), and are fixed, knownquantities, as determined above in connection with FIG. 3. Positioncoordinates 1, 2, 3 represent x, y, z, respectively. The measurements ofthe two ranges r13 and r14 are performed in a similar manner to theequations used by the base station 12 to compute the position of thetransmitter 18.

$\begin{matrix}{{r\; 13} = \sqrt{\left( {{rptrpos}_{13,1} - x_{1}} \right)^{2} + \left( {{rptrpos}_{13,2} - x_{2}} \right)^{2} + \left( {{rptrpos}_{13,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 22} \right) \\{{r\; 14} = \sqrt{\left( {{rptrpos}_{14,1} - x_{1}} \right)^{2} + \left( {{rptrpos}_{14,2} - x_{2}} \right)^{2} + \left( {{rptrpos}_{14,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 23} \right) \\{\delta_{13,14} = {{r\; 13} - {r\; 14}}} & \left( {{Eq}.\mspace{14mu} 24} \right)\end{matrix}$

The difference between the phase measurements (613, 14, Eq. 24), whichis calculated in the hardware (e.g., processor) of the relay station 16in a similar method to those determined at the base station 12, is usedby the base station 12 together with Eq. 5, Eq. 6, and Eq. 7 to solvefor x1, x2 and x3, which represents the x, y, z, position of thetransmitter 18, respectively.

Before the base station 12 can use the computed value for 613, 14, fromequation (Eq. 24), the relay station 16 needs to send the value to thebase station 12. This information is transmitted using the sametransmitter antennae 24-1, 24-2 using standard information transmissionmethods such as used for cellular communication, Wi-Fi, etc., as isknown in the art. Both the base station 12 and the relay station 16contain standard circuitry for performing this operation, which ismultiplexed in at the appropriate setup time while the position-trackingsystem 10 is in a tracking mode.

The relay station 16 is then placed in a mode that allows its twotransmitters 24-1 and 24-2 to transmit distinguishable signals and tothe base receiver antennae 14. As is known in the art, this can take theform of frequency or time multiplexing. Similarly to how the transmitterantenna 18 is located using equations (Eq. 1-Eq. 7), the transmitters24-1 and 24-2 are located using the same equations, but with rangesr5-r8 (FIG. 3) and r9-r12 (FIG. 3), respectively, substituting forranges r1-r4. This provides an x, y, z, position of each transmitter24-1 and 24-2. From the positions of the transmitters 24-1 and 24-2, thelocations of the receiver antennae 22-1, 22-2 can be determined asdescribed in connection with FIG. 3.

FIG. 5 is an embodiment of a process 50 illustrating operating modes ofthe position tracking system 10. When position tracking system 10 isstarted, or when commanded, it enters the selection mode 52. In theselection mode, a mode is selected either to enter normal devicetracking or to set up the relay station 16. If, at step 54, normaltracking is selected, the program enters normal tracking mode 64. Ifinstead, at step 54, the selected mode is to set up the relay station16, the process 50 proceeds to block 56. At block 56, the transmittingantennae 24-1, 24-2 turn on such that transmitting antennae 24-1, 24-2are transmitting on different frequencies from each, as if transmittingantennae 24-1, 24-2 were separate devices being tracked (like a devicewith transmitter 18).

In addition, the base station 12 is set (step 58) to track thetransmitting antennae 24-1, 24-2, and, thus, to determine (step 60)their positions using equations Eq. 8-Eq. 21. The positions of thetransmitting antennae 24-1, 24-2 are saved at the base station 12 sothat equations Eq. 22-Eq. 24 can be utilized to improve trackingperformance. At step 62, the relay station 16 switches over fromgenerating device signatures to transmitting phase difference dataproduced by calculating equations Eq. 22-Eq. 24.

After step 62 completes, or if normal tracking mode has already beenentered, the position-tracking system 10 starts tracking the device(i.e., the device transmitting antenna 18). This tracking isaccomplished by using the base station 12 to obtain (step 66) phasedifference data from signals received by the base receiver antennae 10,processed by phase differencing hardware, and computing phasedifferences as described by equations Eq. 5-Eq. 7. The base station 12also has channels (which may be multiplexed from the base receiverantennae 14, or in parallel) for receiving (step 68) the digital RFencoded data that is coming from the relay station 16, which representsthe phase difference (δ_(13, 14)=r13-r14) measured at the relay station16. Equations for device position computation (for example, Eq. 1-7 andEq. 22-24) are performed in step 70 and another computation cyclerepeats, starting at step 66.

In one embodiment, a wireless relay station 16 is disclosed. Thewireless relay station can be powered by battery or electrical outlet,but the encoded data connection to the base station 12 is completelywireless. In the general embodiment, a single multiplexed antenna orseparate transmit and receive antennae are incorporated at the relaystation. The range of each transmit antenna 24 in the relay station 16is first determined as if it were a normal tracked device. Thisdetermines the range between the relay station 16 and the base station12. For non-concentric transmit/receive antennae, a simple hook andappropriate weight can place the relay station 16, and, therefore, thephysical antennae placement, into a known relationship. More elaborateschemes are detailed in the discussion of FIG. 3. This is all performedin a setup mode, as described previously in the process 50 described inFIG. 5.

After the locations of the relay stations transmitters 24 aredetermined, the range from the transmit antenna 24 of the relay station16 to the base station antennae 14 can be converted to phasemeasurements 6i and used to offset the total range from the device tothe relay station and then to the base station antennae. This providesanother set of equations, as illustrated in equations Eq. 25-Eq. 33.

$\begin{matrix}{{r\; 1} = \sqrt{\left( {{rcvrpos}_{1,1} - x_{1}} \right)^{2} + \left( {{rcvrpos}_{1,2} - x_{2}} \right)^{2} + \left( {{rcvrpos}_{1,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 25} \right) \\{{r\; 2} = \sqrt{\left( {{rcvrpos}_{2,1} - x_{1}} \right)^{2} + \left( {{rcvrpos}_{2,2} - x_{2}} \right)^{2} + \left( {{rcvrpos}_{2,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 26} \right) \\{{r\; 3} = \sqrt{\left( {{rcvrpos}_{3,1} - x_{1}} \right)^{2} + \left( {{rcvrpos}_{3,2} - x_{2}} \right)^{2} + \left( {{rcvrpos}_{3,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 27} \right) \\{{r\; 4} = \sqrt{\left( {{rcvrpos}_{4,1} - x_{1}} \right)^{2} + \left( {{rcvrpos}_{4,2} - x_{2}} \right)^{2} + \left( {{rcvrpos}_{4,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 28} \right) \\{r_{relaystation} = \sqrt{\begin{matrix}{\left( {{rcvr}_{{restation},1} - x_{1}} \right)^{2} +} \\{\left( {{rcvrpos}_{{relaystation},2} - x_{2}} \right)^{2} +} \\\left( {{rcvrpos}_{{relaystation},3} - x_{3}} \right)^{2}\end{matrix}}} & \left( {{Eq}.\mspace{14mu} 29} \right) \\{\delta_{1,{relaystation}} = {{r\; 1} - r_{relaystation} - \Theta_{1}}} & \left( {{Eq}.\mspace{14mu} 30} \right) \\{\delta_{2,{relaystation}} = {{r\; 2} - r_{relaystation} - \Theta_{2}}} & \left( {{Eq}.\mspace{14mu} 31} \right) \\{\delta_{3,{relaystation}} = {{r\; 3} - r_{relaystation} - \Theta_{3}}} & \left( {{Eq}.\mspace{14mu} 32} \right) \\{\delta_{4,{relaystation}} = {{r\; 4} - r_{relaystation} - \Theta_{4}}} & \left( {{Eq}.\mspace{14mu} 33} \right)\end{matrix}$

Here, r1-r4 are again the equations for the base station antennae rangesto the device transmitter 18; r_(relaystation) is the range between therelay station 16 to the device transmitter 18. Additional equations Eq.30-Eq. 33 are now available for incorporating into the trackingsolution. In Eq. 30-Eq. 33, θ_(i) corresponds to wave cycles to preventcycle ambiguity, an example use of which is described in U.S. patentapplication Ser. No. 13/975,724, filed Aug. 26, 2013, and titled “RadioFrequency Communication System,” the entirety of which application isincorporated by reference herein. One way to provide phase measurementor related timing data (calculated from Eq. 30-33) to the base station12 is for the relay station 16 to transmit it on a separate frequency.Additional circuitry at the base station 12 can provide filtering meansto separate this data from direct transmission from the devicetransmitter 18. Other techniques such as spread spectrum encoding anddecoding can be used to allow multiple devices to share limitedbandwidth without interference. Ultra wideband or similar wide spectrumtransmission techniques, comparing time stamped pulsed signals sent fromthe device transmitter to the relay and/or base station, can alsodetermine range and therefore provide O or cycle wave count betweendevice transmitter to the relay station and/or base station receiverantennae.

One of ordinary skill in the art will recognize that labelling the basestation and the relay station is a designer choice. Further, processingof signal data (i.e., the equations above) and consolidation of theresults from different receivers to track an object may be split amongprocessors at the base and relay stations.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method, and computer programproduct. Thus, aspects of the present invention may be embodied entirelyin hardware, entirely in software (including, but not limited to,firmware, program code, resident software, microcode), or in acombination of hardware and software. All such embodiments may generallybe referred to herein as a circuit, a module, or a system. In addition,aspects of the present invention may be in the form of a computerprogram product embodied in one or more computer readable media havingcomputer readable program code embodied thereon.

The computer readable medium may be a computer readable storage medium,examples of which include, but are not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination thereof. As usedherein, a computer readable storage medium may be any tangible mediumthat can contain or store a program for use by or in connection with aninstruction execution system, apparatus, device, computer, computingsystem, computer system, or any programmable machine or device thatinputs, processes, and outputs instructions, commands, or data. Anon-exhaustive list of specific examples of a computer readable storagemedium include an electrical connection having one or more wires, aportable computer diskette, a floppy disk, a hard disk, a random accessmemory (RAM), a read-only memory (ROM), a USB flash drive, annon-volatile RAM (NVRAM or NOVRAM), an erasable programmable read-onlymemory (EPROM or Flash memory), a flash memory card, an electricallyerasable programmable read-only memory (EEPROM), an optical fiber, aportable compact disc read-only memory (CD-ROM), a DVD-ROM, an opticalstorage device, a magnetic storage device, or any suitable combinationthereof.

Program code may be embodied as computer-readable instructions stored onor in a computer readable storage medium as, for example, source code,object code, interpretive code, executable code, or combinationsthereof. Any standard or proprietary, programming or interpretivelanguage can be used to produce the computer-executable instructions.Examples of such languages include C, C++, Pascal, JAVA, BASIC,Smalltalk, Visual Basic, and Visual C++.

Transmission of program code embodied on a computer readable medium canoccur using any appropriate medium including, but not limited to,wireless, wired, optical fiber cable, radio frequency (RF), or anysuitable combination thereof.

The program code may execute entirely on a user's computer, partly onthe user's computer, as a stand-alone software package, partly on theuser's computer and partly on a remote computer or entirely on a remotecomputer or server. Any such remote computer may be connected to theuser's computer through any type of network, including a local areanetwork (LAN) or a wide area network (WAN), or the connection may bemade to an external computer (for example, through the Internet using anInternet Service Provider).

In addition, the described methods can be implemented usingultrawideband for direct range measurement between the device and thebase and relay stations, on an image processing device and/or infraredranging at either the mobile device or at the base and/or relaystations, or the like, or on a separate programmed general purposecomputer. Additionally, the methods of this invention can be implementedon a special purpose computer, a programmed microprocessor ormicrocontroller and peripheral integrated circuit element(s), an ASIC orother integrated circuit, a digital signal processor, a hard-wiredelectronic or logic circuit such as discrete element circuit, aprogrammable logic device such as PLD, PLA, FPGA, PAL, or the like. Ingeneral, any device capable of implementing a state machine that is inturn capable of implementing the proposed methods herein can be used toimplement the image processing system according to this invention.

Furthermore, the disclosed methods may be readily implemented insoftware using object or object-oriented software developmentenvironments that provide portable source code that can be used on avariety of computer or workstation platforms. Alternatively, thedisclosed system may be implemented partially or fully in hardware usingstandard logic circuits or a VLSI design. Whether software or hardwareis used to implement the systems in accordance with this invention isdependent on the speed and/or efficiency requirements of the system, theparticular function, and the particular software or hardware systems ormicroprocessor or microcomputer systems being utilized. The methodsillustrated herein however can be readily implemented in hardware and/orsoftware using any known or later developed systems or structures,devices and/or software by those of ordinary skill in the applicable artfrom the functional description provided herein and with a general basicknowledge of the computer and image processing arts.

Moreover, the disclosed methods may be readily implemented in softwareexecuted on programmed general purpose computer, a special purposecomputer, a microprocessor, or the like. In these instances, the systemsand methods of this invention can be implemented as program embedded onpersonal computer such as JAVA® or CGI script, as a resource residing ona server or graphics workstation, as a routine embedded in a dedicatedfingerprint processing system, as a plug-in, or the like. The system canalso be implemented by physically incorporating the system and methodinto a software and/or hardware system.

Relative terms used herein, such as top, bottom, front, back, side,left, right, above, below, upper, and lower, refer to how features ofthe apparatus appear in the figures, and serve to facilitate thedescription of the invention, and are not meant to be interpreted aslimitations.

While this invention has been described in conjunction with a number ofembodiments, it is evident that many alternatives, modifications andvariations would be or are apparent to those of ordinary skill in theapplicable arts. Accordingly, it is intended to embrace all suchalternatives, modifications, equivalents, and variations that are withinthe spirit and scope of this invention.

What is claimed is:
 1. A method of determining a position of a mobiledevice, the method comprising the steps of: sending, by a first mobiledevice of a plurality of mobile devices, a first wireless transmission;sending, by a second mobile device of the plurality of mobile devices, afirst wireless transmission; receiving, by the first mobile device, thefirst wireless transmission sent by the second mobile device; sending,by the first mobile device, a second wireless transmission that conveysinformation about the first wireless transmission sent by the secondmobile device; calculating a physical position of the first mobiledevice based on the first wireless transmission sent by the first mobiledevice; and calculating a physical position of the second mobile devicebased on the first wireless transmission sent by the second mobiledevice, the calculated physical position of the first mobile device, andthe information about the first wireless transmission sent by the secondmobile device that was conveyed by the second wireless transmission ofthe first mobile device.
 2. The method of claim 1, further comprisingmeasuring, by the first mobile device, a phase difference based on thefirst wireless transmission sent by the second mobile device, andwherein the information about the first wireless transmission sent bythe second mobile device that was conveyed by the second wirelesstransmission of the first mobile device includes the measured phasedifference.
 3. The method of claim 1, further comprising measuring, bythe first mobile device, a phase difference based on the first wirelesstransmission sent by the second mobile device, and wherein theinformation about the first wireless transmission sent by the secondmobile device that was conveyed by the second wireless transmission ofthe first mobile device includes the measured time difference of arrivalinformation.
 4. The method of claim 1, further comprising determiningorientation of the second mobile device.
 5. The method of claim 1,wherein the step of calculating a physical position of the first mobiledevice of the plurality of mobile devices based on the first wirelesstransmission sent by the first mobile device includes the step ofdetermining a physical location of each transmitting antenna of thefirst mobile device relative to each receiver antennae that receives thefirst wireless transmission of the first mobile device.
 6. The method ofclaim 5, wherein each transmitting antenna of the first mobile devicetransmits radio-frequency signals at a different frequency from eachother transmitting antenna of the first mobile device.
 7. The method ofclaim 5, wherein the step of calculating a physical position of thefirst mobile device of the plurality of mobile devices based on thefirst wireless transmission sent by the first mobile device includes thestep of determining a position of each receiver antenna of the firstmobile device with respect to each transmitting antenna of the firstmobile device.
 8. The method of claim 7, wherein the step of determiningthe position of each receiver antenna of the first mobile device withrespect to each transmitting antenna of the first mobile device occursat the first mobile device, and further comprising the step of sendingby the first mobile device the position of each receiver antenna of thefirst mobile device in a third wireless transmission.
 9. The method ofclaim 7, wherein the step of determining the position of each receiverantenna of the first mobile device with respect to each transmittingantenna of the first mobile device includes the step of determining eachposition of that receiver antenna of the first mobile device using aglobal positioning system (GPS).
 10. The method of claim 1, wherein thesecond wireless transmission by the first mobile device that conveys theinformation about the first wireless transmission sent by the secondmobile device occurs over a frequency channel different from a frequencychannel over which the second mobile device sent the first wirelesstransmission.
 11. A position tracking system, comprising: a plurality ofmobile devices, each having at least one transmitter antenna configuredto transmit radio-frequency (RF) signals and at least one receiverantenna configured to receive RF signals; one or more base receivers,each base receiver having at least one receiver antenna configured toreceive the RF signals transmitted by the plurality of mobile devices;and a base station in communication with each base receiver, the basestation having a processor configured to calculate a position of a firstmobile device of the plurality of mobile devices based on a firsttransmission of RF signals by the first mobile device, the processorbeing further configured to calculate a position of a second mobiledevice of the plurality mobile devices based on a first transmission ofRF signals by the second mobile device, on the calculated position ofthe first mobile device, and on a second transmission of RF signals bythe first mobile device that conveys timing information associated withthe first transmission of RF signals by the second mobile device thatwere received by the at least one receiver antenna of the first mobiledevice.
 12. The position tracking system of claim 11, wherein eachtransmission of RF signals is an ultra-wideband transmission.
 13. Theposition tracking system of claim 11, wherein each transmitter antennaof the first mobile device uses a signal-transmission frequency that isdifferent from a signal-reception frequency.
 14. The position trackingsystem of claim 11, wherein the processor of the base station is furtherconfigured to compute a location of each transmitter antenna of thefirst mobile device relative to each receiver antenna of the one or morebase receivers.
 15. The position tracking system of claim 11, whereinthe one or more base receivers includes one base receiver having atleast three base receiver antennae.
 16. The position tracking system ofclaim 11, wherein the one or more base receivers includes at least threebase receivers.
 17. The position tracking system of claim 11, whereinthe base station computes orientation of the second mobile device. 18.The position tracking system of claim 11, wherein the base stationoffsets the information associated with the first transmission of RFsignals sent by the second mobile device by information associated witha distance of the first mobile device from the base station.